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How Medical Components Are Machined and Finished
What each machining process is good at, what it typically holds, the post-processing that follows and which steps your quality system will expect to see validated.
We are a matching service. This page describes what medical machining suppliers commonly run and what to ask them, not a capability of our own.
Machining processes and where they fit
Typical capability, read as a range, never as a promise. The supplier that quotes confirms what it holds on your material, size and feature.
| Process | Part shape | Typical medical parts | Typical capability | What to ask |
|---|---|---|---|---|
| Swiss-type turning | Long, round, small | Bone screws, pins, dental implant bodies and abutments, small shafts | Diameters within ±0.005 to ±0.0125 mm, Ra 0.4 to 0.8 um | Bar diameter range, how thread burrs are removed, in-process gauging |
| Thread whirling | Threaded, slender | Bone screw threads, long slender threads in titanium and stainless | Full thread form in one pass, good flank finish | Whirling or single point, and how the thread is inspected |
| 5-axis milling | Contoured, prismatic | Bone plates, spinal cages, instrument jaws, knee components | ±0.01 to ±0.025 mm on contoured features | Number of setups, fixture design, CMM program per revision |
| Mill-turn | Round with flats | Instrument shafts with flats and cross holes, couplers, robotic parts | ±0.01 mm, features cut in one clamping | Which features are finished without re-clamping |
| Wire EDM | Through profiles | Jaw serrations, slots, nitinol shapes, hardened instrument profiles | ±0.005 mm with skim passes | Skim passes and how the recast layer is removed |
| Sinker EDM | Blind detail | Blind features and fine detail in hardened instrument steels | ±0.01 mm, depends on electrode wear | Electrode material and recast removal |
| Centerless and cylindrical grinding | Round, precise | Pins, guide wires, shafts, trunnions | Roundness of a few micrometres on small diameters | Roundness and taper measurement method |
| Laser tube cutting | Thin wall tube | Nitinol and stainless tube parts, cannulas, flexible sections | Fine kerf, heat affected zone at every edge | Post-cut deburr, electropolish and how the HAZ is treated |
| Polishing and lapping | Any, by surface | Articulating surfaces, instrument faces, cosmetic finishes | Articulating surfaces commonly Ra 0.05 um or better | Whether polishing is manual or controlled, and how Ra is checked |
More on the screw side: bone screw machining at Swiss shops, Swiss turning for device components and thread whirling against single point. On EDM: wire EDM for instrument jaws.
Post-processing and the standard behind it
Name the standard and the method on the drawing. "Passivate" alone gets the cheapest acceptable method and no record you can use.
| Treatment | Standard | Applies to | Note for the drawing |
|---|---|---|---|
| Passivation | ASTM A967, ASTM F86 | Stainless implants and instruments | Nitric or citric acid. No dimensional change. A967 lists the tests that prove it worked. |
| Electropolish | ASTM B912 | 316L, 17-4 PH, nitinol | Removes metal and lowers Ra. Edges round slightly, so tight edges need a note. |
| Titanium anodize | AMS 2488 | Titanium implants and instruments | Type 2 for anti-galling and wear, Type 3 for colour coding by size. |
| Bead or grit blast | Drawing callout | Implant surfaces, non-glare instrument finish | Media type and residue removal belong on the drawing. Embedded media is a contamination question. |
| Heat treatment | AMS 2759, AMS 2801 | 17-4 PH aging, 420 hardening, titanium stress relief | Condition on the drawing, with a hardness check per lot. |
| UDI laser marking | 21 CFR 801.45 | Reusable instruments, implants where marked | Mark after or before passivation changes corrosion behaviour. Decide which, and test it. |
| Cleaning | ASTM F2459 (residue) | Every patient contact part | Coolant and polishing compound residue are what cleaning has to remove. |
Details in passivation and electropolish for medical parts, UDI laser marking and cleaning validation for machined implants.
Verified or validated
A process whose result cannot be fully checked on the finished part has to be validated. That is the rule in clause 7.5.6 of ISO 13485:2016. This is how it usually lands on a machined component.
- MachiningUsually verified by inspection. Validation is often run anyway on implant lines where every feature cannot be measured on every part.
- Deburring and tumblingVerified by inspection at a stated magnification. Burr acceptance needs a written criterion, not a judgement call.
- CleaningValidated. A residue cannot be checked on every part without destroying it, so the process is proven instead.
- Passivation and electropolishValidated, with a lot test from the method in the standard.
- Heat treatmentValidated furnace cycle plus a hardness check per lot.
- Laser welding and markingValidated for weld strength or mark durability after cleaning and reprocessing.
- Sterile barrier sealingValidated to ISO 11607-2 when the supplier packs sterile ready parts. Most component suppliers do not.
Drawing notes that change the quote
Most of the cost in a medical component is decided before the first cut. These are the lines that move it.
- Burr criterionSay where burrs are not allowed and at what magnification they are checked. "Break all edges" on an implant gets you a discussion, not a price. See deburring methods and acceptance.
- Thread specificationBone screw threads to ISO 5835 or a design referenced to ASTM F543 tell the supplier exactly what to gauge.
- Surface finish by featureRa on the bearing, mating or articulating surface, not one value on the title block.
- Recast and heat affected zonesWhether EDM recast or laser HAZ is acceptable and where, so the removal step is quoted.
- Marking content and positionUDI content, location and the stage of the route where it is applied.
- Annual quantityFixtures and validation runs are paid once. A stated annual quantity spreads them properly.
Questions about processes
Swiss turning or 5-axis milling for my part?
Long round parts with threads, such as bone screws, pins and dental implants, are Swiss work. Flat or contoured parts such as plates, cages and jaws are milling work. Parts with both often go to mill-turn. Send the drawing and the supplier choice follows the geometry.
Does machining need IQ, OQ and PQ?
Where the result is fully verified by inspection, validation is not strictly required. Where it is not, it is. In practice implant lines often validate machining as well, and cleaning, passivation and heat treatment are validated almost always. Which steps you require is part of your purchasing controls.
Is wire EDM acceptable on an implant surface?
EDM leaves a thin recast layer. On instruments that is often acceptable. On implant and fatigue loaded surfaces drawings usually require it removed by a stated method, so say whether recast is allowed and how its removal is checked.
Does the supplier do passivation and marking in house?
Some do, many buy them in. We record which steps a shop says it runs itself when it registers, and you should confirm it, because that is where lead time and accountability sit.
Send the drawing with the route on it
We match it with up to 3 machining suppliers whose processes fit and reply within 24 business hours. Grades are on materials, part families on applications, and our checks on how we vet.